1. Field of the Invention
This invention relates to machining fine, precision grooves or cuts in a workpiece. Specifically, it relates to using an abrading wire in reciprocal motion to machine smooth and narrow grooves with precise depths and locations on a workpiece.
One application of the invention relates to machining a pattern of precision grooves on metal tips used in single point and wire bonding.
2. Description of the Prior Art
The prior art has many methods and apparatus for minute machining of a workpiece, e.g, hole enlarging, cutting, dicing, and grinding.
U.S. Pat. No. 2,385,287 discloses a method and apparatus for opening or enlarging the holes drilled in jewel bearings of the type used in precision instruments. A reciprocally moving wire having different diameters in its single length, i.e. a step wire, is advanced through a hole in the jewel until the hole diameter increases to the desired size.
Abrasive particles or grit pre-bonded to continuous elongated tools such as wire-type or band-type blades have been used to cut workpieces. U.S. Pat. No. 4,596,640 discloses a 0.1 millimeter to 1 millimeter diameter tungsten wire, with diamond abrasive particles on its surface, reciprocally moving against a workpiece. Note that 0.1 millimeter is equivalent to approximately 4 mils.
U.S. Pat. Nos. 4,646,710 and 4,727,852 disclose some methods for cutting or subdividing semiconductor wafers. One wafering machine has a bladehead that reciprocally moves a multiplicity of taut wire cutting blades past a workpiece.
U.S. Pat. No. 3,435,815 describes a wafer dicer which subdivides a semiconductor wafer by drawing loops of fine wire across the surface of the wafer to abrade cuts into the wafer surface. The 3 mil to 10 mil diameter wire is continuously transferred from one reel to another in a single direction for a period of time greater than a few minutes. The wire can then be reversed and moved in the opposite direction. An abrasive slurry is fed on to the wire, drawn across the workpiece by the wire, and removed from the wire after the wire passes the workpiece.
U.S. Pat. No. 3,674,004 has a dicing machine that uses an unstressed blade to produce 2 mil cuts in a semiconductor wafer with little or no cutting damage. Cutting elements may have thicknesses of less than 2 mils to thicknesses of 10 to 15 mils. A dimensionally stable and precision cut groove in a cutting assembly holds the blade. The cutting assembly is mounted in a carriage. An alignment assembly has a translation stage moveable in a direction perpendicular to the cutter carriage motion and a rotatable stage mounted on the translation stage platform. A worm gear arrangement rotates the rotatable stage. The alignment assembly aligns the carriage and cutting assemblies relative to the workpiece with a cross hair alignment feature.
The prior art teaches grinding of semiconductor material. U.S. Pat. No. 3,628,294 uses separate grinding wires of progressively smaller diameter to grind out a bevelled cavity in the periphery of a disc of semiconductor material. U.S. Pat. No. 3,834,083 grinds a rounded chamfer on the edge of a workpiece, such as a semiconductor wafer. The workpiece is attached to a revolving chuck. A grinding head, having oblique resilient grinding members, extends beyond the edges of the wafer and presses against wafer the edge.